Hermit Thrushes change their diet in winter, switching from insects and the occasional amphibian, to berries and other fruits.
Think about this. Many North American landbird migrants head south in September and October. Many native North American shrubs, vines and trees offer fruit in September and October. Is there a connection?
Of course there is, and it is just as important in our yards as it is in woods and fields. That connection might be even more important if we want to see and conserve all those thrushes, tanagers and warblers.
Let me tell you about last Halloween weekend in Cape May, N.J. The site experienced one of the epic migratory flights that made it famous in birding circles. Many species were involved, from American Woodcock to raptors, but the signature bird of that flight, we agreed, was Hermit Thrush — Hermit Thrushes overhead in the dark; in the roads at dawn; then in the trees, hedgerows and back yards all over Cape Island; on parked cars; even walking over my boot in the Higbee Beach Wildlife Management Area parking lot.
At one point that Friday, I saw more than a dozen Hermit Thrushes in one binocular view, clustered on a Virginia creeper vine in someone’s back yard — a vine loaded with blue-black fruits. By Sunday, that vine and thousands like it were nearly devoid of berries, but if plants could be happy, those plants were.
Plants bait birds with their fruits, because elderberries, hackberries, gums and company want nothing more than to have migratory birds consume their seeds — consume but not digest. The idea is that the bird benefits from a fleshy fruit meal but "passes” the seed, hopefully far from the mother plant and in a place where the seed can germinate and grow.
It makes sense that plants would evolve fruit timing to coincide with abundant fruit-eating birds on the go and focused on fruit. While nesting in spring and summer, many birds zero in on invertebrate prey for protein and easy digestibility as they nest and feed young.
Spring or summer fruits might wither on the vine, drop or be moved only a short distance or, worst of all from a plant’s perspective, be consumed by insects or mammals that not only digest the fruit but digest or damage the seeds. Come fall, adult birds and their young of the year stream southward, hungry and in a hurry — the perfect seed-dispersal agents.
Keep your eyes open for another pattern: In regions where foliage undergoes a strong seasonal color change in fall, which plant species turn red, and which change color earliest? In my neck of the woods, the Northeast, that would be vines like Virginia creeper and poison ivy as well as trees like dogwoods and black gum — all native, berry-producing species. So close is the bird-fruit link that some plant species fly a flag — red leaves — to signal birds to come and get it.
Of course, not all fruiting plants peak their production in fall. Some, such as junipers and hollies, have fairly persistent fruits important to wintering birds, too. In the West, Townsend’s Solitaires descend from their summer mountain homes to winter on vigorously defended territories in juniper-rich areas, and Yellow-rumped Warblers in the Southeast winter in areas where eastern red cedar (actually a juniper) and bayberries persist.
As humans encroach on natural landscapes, our front and back yards become important surrogate habitats for migrating birds, as do sites like college campuses and city parks. Research suggests that migrant birds are resilient enough to use habitat fragments successfully if the food they need is there.
Fruits provide more than calories for migration. Recent research from University of Rhode Island suggests the same antioxidant vitamins and minerals that help humans fight stress and sickness help birds cope with the stresses of migration.
Come fall, adult birds and their young of the year stream southward, hungry and in a hurry — the perfect seed-dispersal agents.
To help the birds, you really do want fruiting shrubs, vines and trees in your yard. One obvious strategy involves buying and planting native species. Remember, however, that a dogwood from Michigan does not equal a dogwood from Massachusetts. The two might be different species of dogwood, different horticultural varieties or different ecotypes with correspondingly different soil, shade or moisture preferences and fruiting times.
You want the local species if you can get it. Make sure to ask at the nearby nursery exactly which species it offers and their source regions. Fall offers a great time to install woody plants, and online sources such as National Wildlife Federation’s excellent plant lists by region can guide your selection.
An alternative strategy involves leaving corners of your property alone. Simply pay attention to what magically appears there. I recently transplanted three sassafras seedlings obtained for free. Dispersed into my flower bed by birds, they now thrive in a back corner I’ve been trying to fill, along with another volunteer, a holly, I moved there last fall. Also check your friends’ yards; what they might see as weeds could grow into avian treasure for you — and the local and visiting birds.
Want to learn more?
Provide Native Berries To Your Birds
How To Create A Bird-Friendly Garden